Texas Tech researchers responsible for genesis of micro-LED advances

Sep 8, 2017: The patent number is 6,410,940. It is titled “Micro-size LED and detector arrays for mini-displays, hyperbright light emitting diodes, lighting and UV detector and imaging sensor,” and it disclosed a tiny LED with a size around 20 microns (one micron equals one-millionth of a meter), or micro-LED, as well as micro-LED arrays.

The patent was filed more than 17 years ago with several applications imagined by its inventors, Hongxing Jiang and Jingyu Lin. They thought the best use for micro-LEDs would be for small displays and wearable displays that could be used anywhere and would eventually revolutionize the traditional displays and projectors.

“We thought it was interesting to see what kind of new properties would come out of this very small size LED,” Jiang said. “As soon as we started talking about this, then the questions came as to what kind of things you can use from this. We thought about microdisplays and micro-size projectors, we thought about wearable displays and their related applications.”

Shortly after developing micro-LED technology at Kansas State University, Jiang and Lin were recruited by Texas Tech University to occupy the inaugural Edward E. Whitacre Jr. endowed chair and Linda F. Whitacre Endowed Chair, respectively, established by the AT&T Foundation.

They moved their research group, which included research professors, postdoctoral researchers, graduate students and others, along with truckloads of equipment, to Lubbock thanks to the Emerging Technology Fund created in 2005 at the urging of then-Gov. Rick Perry. Today they also are Horn professors in the Edward E. Whitacre College of Engineering and direct the Texas Tech Nanophotonics Center.

Today, micro-LED is one of the fastest-growing technologies in the world as companies utilize it on everything from large-screen televisions to heads-up displays. Even with the upcoming release of the iPhone 8, which is reported to utilize Organic LED (OLED) technology, companies are already moving past that toward micro-LED technology, using it in the next generation of smart phones and televisions.

It just took a couple of decades.

“People are starting to recognize this technology,” Lin said. “They are trying to get it into the smartphones, big and small screens by putting more pixels per area to try to get a higher resolution and higher brightness, while saving power consumption and extending the battery lifetimes of smart phones because micro-LED displays have the advantages of being self-emissive, high efficiency, high brightness and high turn-on/off speed.”

Emergence of LED

The beginning of LED, or Light Emitting Diode, can be traced back to the mid-1960s. LED uses semiconducting materials to produce a diode that emits light when activated by a suitable voltage source. Until the early-1990s, though, LEDs came in just two colors – red and yellow. It wasn’t until about 1993 that blue and green colors were produced, and that enabled the possibility of combining primary colors to produce a white light. That led to the development of LED lightbulbs that are more efficient and use less electricity to produce the same amount of light as an incandescent bulb.

Nowadays, LED lightbulbs are more prevalent, or at least on par with, incandescent lightbulbs in terms of use in households and businesses.

“In the last 20 years, one of the biggest achievements with LED is making them bright enough that they can replace all the lightbulbs,” Jiang said. “You cannot even buy a 100-watt incandescent light bulb anymore because this is an old technology and it is not as efficient. LED is much more efficient and lasts much longer, so it has great advantages.”

But when it comes to displays, televisions and large screens, the term LED can be somewhat misleading.

Most televisions that claim to be LED TVs, the researchers said, actually still use the Liquid Crystal Display, or LCD, that is backlit by white LEDs. What that means is that the background light from a big-screen TV comes from an LED but the display is still LCD. LED light is emitted or blocked to create the dark spots on a screen, or certain colors of LED can be blocked or transmitted to produce color images on the screen.

The technology works the same on smartphone screens. The background is lit by white LEDs and colors are blocked or transmitted in LCD to produce text or color images on the screen.

“In terms of TV applications, all of the commercial LED TVs are using LEDs as backlight,” Lin said. “The display is still LCD. They’re not using micro-LEDs yet.”

But it’s coming.

Evolution of LED

While regular LED light comes from inorganic semiconductors, practical OLED technology began to emerge during the last decade. Naturally, OLED uses organic semiconducting material to produce light.

MOCVD

The most visible form of OLED comes in flexible displays, which several companies are developing. While efficient and self-emissive, OLED is also very expensive, with large-screen televisions priced anywhere from $3,000 to $9,000, depending on size.

The biggest issue with OLED is it has a shorter lifetime and lower brightness than regular LED, similar to the problems plasma televisions encountered when they first came on the market.

While the world was looking to OLED to bring larger displays, Jiang and Lin were more interested in the novel applications of micro-LEDs.

“We want to make everything very compact,” Lin said. “The only thing limiting us is the screen. We have already made prototype microdisplays, but they are monochrome, green and blue, and can project images. But it’s not full color yet.”

The push for micro-LED

While the iPhone 8 is expected to be the first Apple device to incorporate an OLED display, the company already has made moves to advance past OLED to micro-LED. One development, which Jiang identified as one of the two most important moves in micro- LED proliferation, was the purchase by Apple of LuxVue Technology in 2014 to research making micro-LED displays commercially viable for iPhones and other potential products.

Another interesting development Jiang identified is that some companies are currently working on making giant displays or television screens using micro-LED technology to provide ultra-high brightness, resolution, contrast and turn-on/off speed. He noted Sony has made some strides in that area, and several other companies are interested in developing the technology for their own products.

Jiang and Lin can see a time, eventually, when micro-LED technology could shrink and eliminate a computer or phone screen altogether.

“We demonstrated the principle of micro-LED technology 17 years ago that you can use them to make microdisplays, where you can wear them,” Jiang said. “We were also developing this technology for projection. You can display all the information on a wall, on a window, on a car windshield. In principle, you can also make something like this where the applications allow you to wear something like a Goggle Glass for the projection, or you can have a very small device, like a pen, that can project the images.”

As for what the future holds, both speculated emerging three-dimensional (3-D) and AR, or augmented reality, micro-LEDs, with their outstanding properties, especially high turn on/off speed, could be the next to become part of the mainstream. They also feel the surface of micro-LED technology has just been scratched.

The research and development efforts of Jiang and Lin, and all their current and former research colleagues, have already made an impact on society. They did so sometimes without knowing exactly what kind of real products their discoveries might lead to. However, that is the essence of research and development. Who knows what today’s discovery will lead to tomorrow?

“Many research projects fail to deliver a real product, but there are always a certain fraction that succeed in creating practical applications with a long lasting impact,” Lin said. “That’s why it’s extremely important we invest in science even though the probability of getting a real product is small. It’s real, and that’s why people cannot say ‘it is a waste of time or a waste of money for this research.’ If you don’t do it at all, then nothing will ever come out of it.”